The presence of components capable of active immunosuppression has been often demonstrated in human serum drawn from patients admitted for thermal injury, trauma, and advanced cancer. Attempts to isolate and identify such immunosuppressive components have usually implicated peptides associated with serum alpha-globulins as the active agents (i.e., immunoregulatory alpha-globulin or IRA bound proteins). Further resolution of specific regulatory peptides and the determination of possible therapeutic countermeasures has been frustrated by the difficulty in obtaining large enough quantities of specific materials for chemical and immunological identification. We feel that while such analyses at the molecular level are indeed important, such procedures are not necessary to answer some of the fundamental functional questions concerning these serum immunosuppressives. To this end we propose to collect and pool human serum drawn from patients with advanced cancer, which displays strong immunosuppressive activity in vitro. Activity will then be reconfirmed in vivo by passive transfer of plasma C3H/HeJ mice. Primary hemolytic response to sheep erythrocytes (Jerne plaque technique) and ability to reject Balb/C (H-2d to H-2K) skin allografts or testicular interstitial (Leydig cell) tumor fragments implanted subcutaneously after serum transfer will be compared with normal animal responses. The presence of alpha-globulin associated peptides or other immunosuppressive serum proteins will be sought by 2-dimensional electroimmunodiffusion, and possible immunosuppressive serum subfractions identified by comparison with diffusion patterns of normal serum. Antiserum will be prepared in rabbits specific to each elevated serum component using the ingenious technique recently described by Crowle. Mice will then be tested as above for hemolytic response, skin and tumor graft acceptance after receiving both the immunosuppressive serum and specifically prepared antibody. Antibody capable of cancelling the immunosuppressive qualities of cancer-derived serum will then be reacted with immunosuppressive serum and the resulting antigen-antibody complex dissociated isolating the immunosuppressive agent in quantity. Immunosuppressant thus isolated will be further tested in mice for ability to alter hemolytic and allograft responses, then FITC labeled and traced in vivo after injection.